1. Field of the Invention
This invention relates generally to pavement markers, and is particularly concerned with pavement markers of the type that utilize retrodirective reflecting elements, such as cube-corner reflector elements, for reflecting light from vehicles traveling over the roadway surface on which the pavement marker is secured. The invention also is concerned with the construction of a high strength reflector assembly, particularly, but not exclusively, useful in pavement markers.
2. Description of the Prior Art
U.S. Pat. Nos. 3,332,327 and 3,409,344 disclose pavement markers having retrodirective reflector elements of the cube-corner type formed thereon. The cube-corner reflector elements are formed on an outer wall of the pavement marker, which outer wall is frequently engaged by the wheels of vehicles traveling over the roadway. In order to provide adequate strength to withstand the forces imposed by the vehicle wheels, the pavement marker bodies are filled with epoxy resin or the like. In order to protect the cube-corner reflector elements from moisture and chemical attack, the surface of the reflector elements are metallized. While the metallized layer performs the function of protecting the reflector elements, is also causes a loss of optical efficiency. The loss of optical efficiency can be as high as 50%.
U.S. Pat. Nos. 3,627,403 and 3,784,279 disclose pavement markers wherein a sheet of flexible plastic material is interposed between the cube-corner reflector elements and the resin fill to protect the reflector elements from moisture and chemical attack. It is difficult to assemble the flexible plastic sheet in the pavement marker with presently known manufacturing methods; hence, the manufacturing costs of such pavement markers have thus far been excessive.
U.S. Pat. No. 3,485,148 discloses a pavement marker wherein groups of cube-corner reflector elements are enclosed in cells by integral walls formed on the reflector body and surrounding each of the cells. The walls support the reflector body on a high strength metal housing. While the walls provide strength to the reflector body, the walls provide no reflectivity for vehicle lights. Consequently, the total number of reflector elements, and hence the overall reflectivity of the reflector body is substantially reduced.
Reflectors for marking the sides of landing strips, roadways, and for use on bicycles and motor vehicles, such as disclosed, for example, in U.S. Pat. Nos. 3,541,606; 3,545,839 and 3,781,082, are frequently subject to damage by the impact of stones, pebbles and the like on the outer face of the reflector. Usually, such reflectors have unsupported walls on which the retrodirective reflector elements are formed. The unsupported walls have low resistance to impact forces.